The Mainz Cathedral
When History Hangs in the Air – A Glimpse into Its Chemical Scent Signature
The Mainz Cathedral is not only an impressive building of historical and cultural importance but also a unique space for investigation. The air inside such a structure carries the traces of its materials, its history, and its use. Old wood, masonry, paints, restoration materials, but also candle smoke, incense, or visitor activities leave behind volatile substances that can be detected with sensitive measuring techniques.
The indoor air was collected using sorptive materials and later analyzed in the laboratory with thermal desorption and gas chromatography–mass spectrometry (TD-GC-MS). (Photo: Alexandra Gutmann)
As part of our project D2Smell, we recorded emission spectra inside the Cathedral — both during regular day-to-day operation and after special religious holidays. The aim is to use chemical analysis to understand which organic compounds are present in the indoor air — and what they can tell us about the past and present of this place.
Scents are closely tied to places and to the stories that unfold within them. In Mainz, the Cathedral is such a place — shaping the cityscape, everyday life, and many special moments. Because of its significance, its characteristic scent — represented here by incense — has also found its place on our City Scent Map.
The Scentscape of the Mainz Cathedral
The chromatogram below shows the composition of the volatile organic compounds (VOCs) detected in the Cathedral’s indoor air. Unlike floral scents, these substances originate from a wide variety of sources: building materials, organic aging processes, cleaning agents, candles, or liturgical fragrances such as incense.
Depiction of the volatile organic compounds (VOCs) found in the Cathedral’s indoor air. The peaks represent individual substances — aldehydic, aromatic, and terpenoid compounds. On January 6 (Epiphany), the chromatogram (red), compared to the everyday profile (black), shows additional signals of typical incense components originating from the festive liturgy. (Measurement and processing: Kathleen Raap)
We were able to identify a series of characteristic substances that allow conclusions about their sources:
🪵 Furfural & Hexanal
These two aldehydes are formed during the aging of wood or textiles and point to historical building materials or furnishings inside the Cathedral. They are typical markers of organic decomposition processes of wooden interiors.
🌼 α-Pinene & Nonanal
Two substances that reflect everyday life inside the Cathedral. α-Pinene is a characteristic monoterpene of coniferous wood. Its fresh, resinous scent recalls a pine forest. Nonanal, on the other hand, carries a waxy, citrus-like odor and can arise both from the degradation of organic materials and from perfume oils — or even from the presence of people themselves.
🕯️ Decane
Candlelight leaves behind more than just brightness — it also leaves traces in the air. Decane is a long-chain alkane found in paraffin products such as candles and waxes. It is hardly noticeable by smell, but it contributes a subtle “warm” base note.
🎨 Xylole & Ethylbenzol
These aromatic compounds usually originate from paints, varnishes, and adhesives. They point to restoration work or to older coatings that still release small amounts of volatile substances. They may also be produced by candle burning.
🧴 Acetic Acid
A simple yet striking compound, sharply sour and unmistakably vinegar-like. While we collected our samples early in the morning, cleaning was already underway elsewhere in the cathedral. Although we did not perceive the smell at our measuring spot, our instruments certainly did. Acetic acid, however, does not only come from cleaning agents – it is also emitted by humans through breath and skin. What we captured may therefore have been the subtle remains of the visitors from the previous day. Learn more on our project page on human scent emissions.
Insence – The Scent of Special Moments
On major religious holidays, the atmosphere inside the Cathedral changes noticeably. Visitors enter—often more quietly than usual—with a sense of anticipation, as if the moment itself stands apart from everyday life. The scent is an essential part of this experience.
When incense is used, it fills the space with a dense, warm character. Resinous, slightly sweet, and fresh notes overlay the otherwise rather restrained background of the Cathedral. For a while, everything else recedes—the space takes on a new and clearly perceptible identity.
🌿 Linalool & Octyl Acetate
These two compounds are typical constituents of incense resins. Linalool has a floral, fresh, slightly citrus-like scent, while octyl acetate contributes soft, fruity notes. Both compounds were detected not only in pure incense but also in the air samples from the Cathedral.
🔥 Toluene
In addition to these original components, compounds also appear that are formed during burning. Toluene is a typical example. It belongs to the group of aromatic compounds and is produced through thermal processes when incense is smoldered. Its presence shows that the measured profile reflects not only the resin itself but also its transformation through heat.
What Shapes a Scent – Between Measurement and Perception
It is striking that some peaks in the chromatogram appear comparatively small—yet they can be highly significant in terms of smell.
This becomes particularly clear when comparing linalool and acetic acid. Acetic acid often produces a much larger signal in the chromatogram but frequently remains below the perception threshold in the indoor air. Despite its analytical presence, it contributes little to the actual odor impression. Linalool behaves in the opposite way: it is usually present at much lower concentrations but has a very low odor threshold. Even small amounts are sufficient to be perceived and to shape the overall scent character.
The size of a peak therefore says little about how strongly a substance influences what we smell—what matters is how sensitive our nose is to it. Especially in complex mixtures, it becomes clear that analytical data alone are not enough to fully capture the scent of a place. Descriptions by people are an essential complement: they help link measured compounds to actual sensory perception.
If you would like to help us connect scent descriptions with measurement data, you can take part in our Scent Incognita project. There, we collect perceptions and impressions that help us better understand the chemical profile of places.
The presence of these substances in the Cathedral’s air is a chemical expression of lived practice — like an invisible record. They reveal what has taken place there and give the Mainz Cathedral its own unmistakable scent. Its scent is therefore just as much a part of the city’s identity as its architecture — and this is why the Cathedral is also represented on our City Scent Map.
Text: Alexandra Gutmann